ltc3557-ltc3557-1 Linear Technology Corporation, ltc3557-ltc3557-1 Datasheet - Page 12

• Manufacturer Part Number: ltc3557-ltc3557-1
• Description: Usb Power Manager With Li-ion Charger And Three Step-down Regulators
• Manufacturer: Linear Technology Corporation

LTC3557/LTC3557-1
Introduction
The LTC3557/LTC3557-1 is a highly integrated power
management IC that includes a PowerPath controller,
battery charger, an ideal diode, an always-on LDO, three
synchronous step-down switching regulators as well as
a buck regulator V
USB applications, the PowerPath controller incorporates
a precision input current limit which communicates with
the battery charger to ensure that input current never
violates the USB specifi cations.
The ideal diode from BAT to V
power is always available to V
fi cient or absent power at V
The LTC3557/LTC3557-1 also has the ability to receive
power from a wall adapter or other non-current-limited
power source. Such a power supply can be connected to
the V
ternal device such as a power Schottky or FET as shown
in Figure 1.
OPERATION
12
OUT
FROM
USB
pin of the LTC3557/LTC3557-1 through an ex-
FROM AC ADAPTER (OR HIGH VOLTAGE BUCK OUTPUT)
24
3
WALL
V
BUS
C
(FALLING)
controller. Designed specifi cally for
(RISING)
4.3V
3.2V
BUS
+
–
OUT
75mV (RISING)
25mV (FALLING)
OUT
–
+
+
–
.
guarantees that ample
even if there is insuf-
Figure 1. Simplifi ed PowerPath Block Diagram
USB CURRENT LIMIT
FOR HIGH VOLTAGE BUCK REGS
LT3480, LT3481 OR LT3505
ENABLE
OPTIONAL CONTROL
26
V
C
CONSTANT CURRENT
CONSTANT VOLTAGE
BATTERY CHARGER
The LTC3557/LTC3557-1 has the unique ability to use
the output, which is powered by an external supply, to
charge the battery while providing power to the load. A
comparator on the WALL pin is confi gured to detect the
presence of the wall adapter and shut off the connection
to the USB. This prevents reverse conduction from V
to V
The LTC3557/LTC3557-1 provides a V
can be used to drive the V
buck switching regulator such as the LT3480, LT3481, or
LT3505 to provide power to the V
circuitry adjusts the regulation point of the switching
regulator to a small voltage above the BAT pin voltage.
This control method provides a high input voltage, high
effi ciency battery charger and PowerPath function.
An “always on” LDO provides a regulated 3.3V from V
This LDO will be on at all times and can be used to supply
up to 25mA.
BUS
V
when a wall adapter is present.
BAT
OUT
DIODE
IDEAL
–
+
15mV
+
–
ACPR
C
GATE
V
BAT
OUT
pin of an external high voltage
35571 F01
25
23
21
22
OUT
+
pin. The V
C
Li-Ion
output pin which
OPTIONAL
EXTERNAL
IDEAL DIODE
PMOS
SYSTEM
LOAD
C
control
35571fa
OUT
OUT
.